Gas chromatographic separation of aromatic mixtures

ABSTRACT

A mixture of C8 aromatics, ethylbenzene, ortho-xylene, metaxylene and para-xylene is separated into its component parts by production gas chromatography. The mixture is passed with a carrier in contact with a certain zeolite to separate the paraxylene and ethylbenzene by different sorption rates and the remaining mixture of meta- and ortho-xylene is contacted with a liquid partitioning agent to separate the ortho-xylene and metaxylene by different sorption rates.

United States Patent [451 Apr. 18, 1972 Drinkard et al.

[54] GAS CHROMATOGRAPHIC SEPARATION OF AROMATIC MIXTURES 72 Inventors:B. M. Drinkard; Paul T. Allen; Edward H.

Unger, all of Beaumont, Tex.

[73] Assignee: Mobil Oil Corporation [22] Filed: June 8, 1970 [21] Appl.No.: 44,460

[52] US. Cl ..55/67, 55/75 [51] Int. Cl ..B0ld 15/08 [58] Field ofSearch ..73/23.l;210/31,198;55/67,

[56] References Cited UNITED STATES PATENTS l RQb tmnH I' !YHY' VI 'II'FHIISS/197 x Primary Examiner-Jim L. DeCesare Attorney-Oswald G. Hayesand Andrew L. Gaboriault [57] ABSTRACT A mixture of C3 aromatics,ethylbenzene, ortho-xylene, metaxylene and para-xylene is separated intoits component parts by production gas chromatography. The mixture ispassed with a carrier in contact with a certain zeolite to separate thepara-xylene and ethylbenzene by different sorption rates and theremaining mixture of metaand ortho-xylene is contacted with a liquidpartitioning agent to separate the ortho-xylene and meta-xylene bydifferent sorption rates.

12 Claims 1 Drawing Figure PATENTEDAPR 18 m2 3, 656 278 VINVENTORS B. M.DRINKARD, P.. T. ALLEN 8; E. H. UNGER BY AT'ILORNEY GAS CHROMATOGRAPIIICSEPARATION OF AROMATIC MIXTURES BACKGROUND OF THE INVENTION 1. Field ofthe Invention This invention relates to the gas chromatographicseparation of C aromatic mixtures and more particularly to a gaschromatographic method for the separation of a mixture of ethyl-benzene,ortho-xylene, meta-xylene and para-xylene into itscomponent parts.

2. Description of the Prior Art Gas chromatography, as a method for theseparation of mixtures of difficulty separable materials, has been wellknown for some time. In general, the method operates on the principle ofdistribution of the components of a sample over separate phases andsubsequent separation of these phases. For example, in gas-liquidchromatography, the volatile components of a sample are distributedbetween an inert gas phase (carrer gas) and a stationary liquid.Similarly in adsorption chromatography, there is obtained sampledistribution over a solid adsorbent and a moving liquid phase. Columnspacked with the stationary liquid or solid adsorbent are usuallyemployed to effect the separations by passage of the mixture to beseparated and carried therethrough. Hence, chromatography is a physicalmethod of separation in which the components to be separated aredistributed between two phases, one of the phases constituting astationary bed of large surface area, the other being a fluid thatpercolates through or along the stationary bed.

While chromatography has been applied to the separation of manydifficulty separable mixtures with great success, the separation ofclose-boiling isomeric mixtures has not been particularly successful.One such mixture is C aromatics and especially a mixture ofethylbenzene, ortho-xylene, metaxylene and para-xylene, particularly ona production scale and in a very high state of purity. Para-xylene, inparticular, is required in a very high state of purity for themanufacture of terephthalic acid which is an intermediate in themanufacture of synthetic fibers such as Dacron." Normally it isseparated from a product stream containing ethylbenzene, meta-xylene andortho-xylene by costly superfractionation and multistage refrigerationsteps. This process involves high operation costs and has a limitedyield.

It has also long been known that porous substances such as silica gel,activated char, and certain zeolites, have certain selective adsorptioncharacteristics useful in resolving a hydrocarbon mixture into itscomponent parts. Thus, silica gel is selective in removing aromatichydrocarbons from non-aromatic hydrocarbons and activated chars areuseful in separating oleiins from mixtures with paraffins. Similarly,the molecular sieve properties of zeolites have been utilized toselectively remove one molecular species from a mixture of the same withother species.

Although a wide variety of zeolitic materials, particularly crystallinealuminosilicates, have been successfully employed in various separationschemes, nevertheless, these prior art processes,in general, fell intoone or two main categories. In one type, a zeolite is employed having apore size sufficiently large to admit the vast majority of componentsnormally found in a process stream. These molecular sieves are referredto as large pore zeolites and they are generally stated to have a poresize of about l3A., such as zeolite X, Y, and L. The other type ofcrystalline aluminosilicates are those having a pore size ofapproximately 5A. which are utilized to separate small molecules such asn-paraffms to the substantial exclusion of other molecular species. Thezeolites of these types, however, have not been found capable ofeffectively separating the close-boiling C aromatics.

Another proposed solution to this problem is set forth in US. Pat. No.3,126,425. This patent discloses contacting a mixture of xylene isomerswith crystalline aluminosilicates such that the orthoand metaisomers aresorbed by said aluminosilicates and the para-isomer is concentrated inthe unabsorbed portion. This method is concerned with the concentrationof the more symmetrical disubstituted aromatic isomer, such aspara-xylene, in the unadsorbed stream. It therefore apparentlyrepresents an extension of the normal relative partitioning of xyleneisomers with high surface area solids to the more selective crystallinealuminosilicate surface. All of the isomers described in the abovepatent will be sorbed by crystalline aluminosilicates having uniformpore openings of l0-l3 Angstrom units. The separations shown aretherefore not dependent on the molecular sieving properties of the 13Angstrom zeolite, but rather, on the relative partitioning of the saidisomers between the intracrystalline sorbed phase and the free liquidphase. This method is therefore severely limited and may as stated byrestricted because of economic considerations to processing only streamscontaining 50% or more para-xylene. The normal concentration ofparaxylene in equilibrium mixtures of xylene isomers obtained fromcommercial isomerization units is generally about 24 weight percent sothat this method will not accomplish the desired separation on feedssuch as this.

In still a later development by applicants assignee. it was discoveredthat selective separations of this type can be achieved by utilizing aunique class of crystalline aluminosilicates which possess uniquemolecular sieving properties in that they allow entry and egress totheir internal pore structure of not only normal paraffms but also ofslightly branched paraffins and yet have the ability to effectivelyexclude paraffins possessing quaternary carbon atoms at short contacttimes. These zeolites also possess the ability to selectively sorbsimple, lightly-substituted monocyclic hydrocarbons from mixedhydrocarbon streams containing highly substituted monocyclic,polycyclic, heterocyclic or even simple polycyclic hydrocarbons. Thesezeolites :also possess the unique property of selectively sorbingl,4-disubstituted aromatic compounds in admixture with l,2,l,3-, or morehighly substituted aromatic hydrocarbons. Para'xylene, for example, canbe selectively separated from orthoand meta-xylene by contacting saidmixture with this unique class of zeolites. This discovery is fullydisclosed and claimed in copending J. Cattanach application Ser. No.882,692, filed Dec. 5, 1969, of applicants assignee.

The process of the present invention represents an improvement on theprocess disclosed in copending application Ser. No. 882,692 in theseparation of a mixture of ethylbenzene, ortho-xylene, meta-xylene andpara-xylene into its component parts by utilization of the specialmolecular sieves in combination with a second liquid partitioningchromatography separation.

SUMMARY OF THE INVENTION In satisfaction of the foregoing objects andadvantages,

there is provided by this invention a process for the separation of amixture containing ethylbenzene, ortho-xylene, metaxylene andpara-xylene into its component parts comprising contacting said mixturewith a certain crystalline zeolite material for a period of time toseparate the ethylbenzene and para-xylene, and passing the remainingmixture of orthoxylene and meta-xylene in contact with the carrier and astationary liquid to separate the ortho-xylene and meta-xylene, andrecovering the separated components.

BRIEF DESCRIPTION OF THE DRAWING Reference is now made to the drawingaccompanying this application wherein there is set forth a suitablediagram of an apparatus for conducting the process of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS The process of the presentinvention has been found to provide a chromatographic process for Caromatic separation that eliminates para-xylene crystallizers,ethylbenzene and ortho-xylene fractionating columns and still producesquantitative recovery of high purity components. A special advantage ofthe chromatographic process of this invention is that it is suitable foreffecting the separations on a production scale.

As indicated, the process utilizes a two-step chromatographic separationof the mixture of ethylbenzene, orthoxylene, meta-xylene and para-xyleneinto its component parts. In this process, the mixture, which generallyis a feed reformate from a commercial unit, either as a gas, liquid ormixed phase, is preferably contacted with a suitable fluid carrier,typical carriers including steam, water, nitrogen, air, helium,hydrogen, hydrocarbons, alcohols, ketones, etc. and then contacted withthe zeolite in the first step. Conveniently, contact with the zeoliteand also the chromatographic liquid partitioning agent in the secondstep, is carried out in columns, that is, the zeolite and liquidpartitioning agent are maintained in separate columns and thefeed/carrier mixture is passed therethrough. In general, the columncontaining the adsorbent is about twenty times larger in diameter thanthe zeolite column although this may be varied depending on otherconditions of the process. The separated components-are then recoveredon elution.

The composition of a typical feed mixture for the process in parts byweight is preferably as follows:

Component Amount wt. 71 Ethylbenzene -l5 (LTI) Para-xylene 20-30Meta-xylene 40-50 Ortho-xylene -25 In the first step of the process, thefeed mixture is contacted with a suitable carrier, as described above,and passed into the zeolite-containing column. In this column, thepara-xylene and ethylbenzene are separated from the mixture of orthoandmeta-xylene. This occurs by reason of the different rates of sorption ofthe components. In this process, the mixture of orthoand meta-xylenes isemitted first from the column as passage of the mixture is generallyuninhibited by the zeolite and is passed to the second stage.Thereafter, para-xylene, 99% purity, is emitted, followed by 99% pureethylbenzene, the latter two components thus being recovered in highpurity and quantitative yields. Hence the rate of progress ofpara-xylene through the column is faster than ethylbenzene.

The remaining mixture of orthoand meta-xylenes is then transmittedthrough the second column containing the standard liquid partitioningphase substance together with the carrier. In this column the twocomponents of the mixture are separated to provide initially themeta-xylene in 99% purity and thereafter the ortho-xylene in 99% purity,both in substantially quantitative yields. In this column, themeta-xylene is sorbed at a slower rate than the ortho-xylene.

The process may be better understood by reference to the drawingaccompanying the application wherein numeral 1 denotes a reformate feedof the above composition being introduced into feed tank thence by line2 to vessel where it is admixed with the carrier from line 3.Conveniently, the carrier is helium or steam, although others may beused, as described above, and vessel 30 is a vaporizer.

The mixture then passes via line 4 into zeolite-containing column 40 forthe initial separationfAs indicated above, the adsorbent-containingcolumn is generally about twenty times larger in diameter than thisinitial zeolite-containing column. In column 40, after about twominutes, a mixture of metaand ortho-xylenes is emitted via line 5 and istaken off by line 6 for transmission to the second column. Thereafter,in the period of about three to five minutes, para-xylene is emitted vialine 5 and is taken off by line 7. Finally, in the period of about 5 to8 minutes, ethylbenzene is emitted via line 5 and is taken off by line8.

In the meantime, the mixture of metaand ortho-xylenes in line 6 is sentfor passage through column 50 which contains the standardchromatograph-type liquid partitioning agent. From column 50, it will beobserved that in the period of about 9 to 12 minutes, meta-xylene isemitted via line 9 and is taken off by line 10. Thereafter, in theperiod of about thirteen to 14 minutes, the ortho-xylene is emitted vialine 9 and is taken off by line 11. All of the time periods mentionedfor removal of each material are cumulative based on the time at whichthe entire mixture is initially introduced into zeolite column 40, andare dependent on the conditions of the chromatographic process, i.e.,temperature, carrier flow, length of column, etc.

As indicated above, the zeolites utilized in the first column are of aspecial type and are disclosed and claimed for use in a novel zeolitechromatographic process in copending application Ser. No. 882,692, filedDec. 5, 1969 of .I. Cattanach of the same assignee. Generally, thesezeolitic materials allow selective separations to be achieved dependingon either the size, shape or polarity of the sorbate molecules. Thisclass of novel crystalline aluminosilicates can generally be stated tohave intermediate shape-selective sorption properties. The unique natureof this novel class of zeolites is characterized by the presence ofuniform pore openings which are apparently elliptical rather thancircular in nature. The effective pore openings of this unique class ofzeolites have both a major and minor axis, and it is for this reasonthat the unusual and novel molecular sieving effects are achieved. Theunique type of molecular sieving produced has generally been referred toas a keyhole molecular sieving action. From their dynamic molecularsieving properties it would appear that the major and minor axis of theelliptical pore in this family of zeolites have effective sizes of about7.0 07A. and 5.0 1- 0.5A., respectively.

The family of ZSM-5 type compositions, useful in the novel process ofthis invention, has the characteristic X-ray diffraction pattern setforth in Table l, hereinbelow. ZSM-S compositions can also beidentified, in terms of mole ratios of oxides, as follows:

wherein M is a cation, n is the valence of said cation, W is selectedfrom the group consisting of aluminum and gallium, Y is selected fromthe group consisting of silicon and germanium, and Z is from 0 to 40. Ina preferred synthesized form, the zeolite has a formula, in terms ofmole ratios of oxides, as follows:

and M is selected from the group consisting of a mixture of alkali metalcations, especially sodium, and tetraalkylammonium cations, the alkylgroups of which preferably contain two to five carbon atoms.

In a preferred embodiment of ZSM-5, W is aluminum, Y is silicon and thesilica/alumina mole ratio is at least 10 and ranges up to about 60.

Members of the family of ZSM-5 zeolites possess a definitedistinguishing crystalline structure whose X-ray diffraction patternshows the following significant lines:

TABLE I lnterplanar Spacing d(A) Relative Intensity l M t 0.2 S 10.0:0.2 S 7.4 i 0.15 W 7.1 x 0.15 W

6.3 z 0.1 6.04 t 0.1 5.97 z 0.] 5.56 i 0.1 5.01 i 0.1 4.60 i 0.08 4.25 10.08 3.85 t 0.07 3.7] t 0.05 3.64: 0.05 3.04 I 0.03 2.99 0.02 2.94 i0.02

zsszmfisssssss y and the positions as a function of two times theta,where theta is the Bragg angle, were read from the spectrometer chart.From these, the relative intensities, 100 M, where I is the intensity ofthe strongest line or peak, and d (obs), the interplanar spacing in A,corresponding to the recorded lines, were calculated. In Table I therelative intensities are given in terms of the symbols S strong, Mmedium, MS medium strong, MW medium weak and VS very strong. It shouldbe understood that this X-ray diffraction pattern is characteristic ofall the species of ZSM-5 compositions. Ion exchange of the sodium ionwith other cations reveals substantially the same pattern with someminor shifts in interplanar spacing and variation in relative intensity.Other minor variations can occur depending on the silicon to aluminumratio of the particular sample, as well as if it had been subjected tothermal treatment. Various cation exchanged forms of ZSM-5 have beenprepared. X-ray powder diffraction patterns of several of these formsare set forth below. The ZSM-S forms set forth below are allaluminosilicates.

TABLE 2 X-Ray Diffraction ZSM-S Powder in Cation Exchanged Forms dSpacings Observed Made HCl NaCl c6131 REC], A No, 11.15 11.16 11.1911.19 11.19 11.19 10.01 10.3 10.05 10.01 10.06 10.01 9.74 9.78 9.80 9.749.79 9.77 9.01 9.02 8.99 8.06 7.44 7.46 7.46 7.46 7.40 4.46 7.08 7.077.09 7.11 7.09 6.70 6.72 6.73 6.70 6.73 6.73 6.36 6.38 6.38 6.37 6.396.37 5.99 6.00 6.01 5.99 6.02 6.01 5.70 5.71 5.73 5.70 5.72 5.72 5.565.58 5.58 5.57 5.59 5.58 5.37 5.38 5.37 5.38 5.37 5.13 5.11 5.14 5.125.14 4.99 5.01 5.01 5.01 5.01 5.01

Zeolite ZSM-S can be suitably prepared by preparing a solutioncontaining tetrapropyl ammonium hydroxide, sodium oxide, an oxide ofaluminum or gallium, an oxide of silica or germanium, and water andhaving a composition, in terms of mole ratios of oxides, falling withinthe following ranges:

TABLE 3 Particularly Broad Preferred Preferred OH lSiO 0.07-[.0 0.1-0.80.2-0.75 R.N+/( 1N +Na) 0.2-0.95 0.3-0.9 0.4-0.9 H,O/0H' 10-300 10-30010-300 YO /W 0 5-IO0 10-610 l0-40 wherein R is propyl, W is aluminum orgallium and Y is silicon or germanium, maintaining the mixture untilcrystals of the Zeolite are formed. Thereafter, the crystals areseparated from the liquid and recovered. Typical reaction conditionsconsist of heating the foregoing reaction mixture to a temperature offrom about C to 200 C for a period of time of from about 6 hours to 60days. A more preferred temperature range is from about to C with theamount of time at a temperature in such range being from about 12 hoursto 8 days.

The digestion of the gel particles is carried out until crystals form.The solid product is separated from the reaction medium, as by coolingthe whole to room temperature, filtering, and water washing.

The foregoing product is dried, e.g., at 230 F, for from about 8 to 24hours. Of course, milder conditions may be employed if desired, e.g.,room temperature under vacuum.

ZSM-S is preferably formed as an aluminosilicate. The composition can beprepared utilizing materials which supply the appropriate oxide. Suchcompositions include for an aluminosilicate, sodium aluminate, alumina,sodium silicate, silica hydrosol, silica gel, silicic acid, sodiumhydroxide and tetrapropylammonium hydroxide. It will be understood thateach oxide component utilized in the reaction mixture for preparing amember of the ZSM- family can be supplied by one or more initialreactants and they can be mixed together in any order. For example,sodium oxide can be supplied by an aqueous solution of sodium hydroxide,or by an aqueous solution of sodium silicate; tetrapropylammonium cationcan be supplied by the bromide salt. The reaction mixture can beprepared either batchwise or continuously. Crystal size andcrystallization time of the ZSM-S composition will vary with the natureof the reaction mixture employed. ZSM5 is disclosed and claimed in Ser.No. 865,472,, filed Oct. 10, 1969.

Another operable zeolite falling within the above class is zeolite ZSM-8which is described and claimed in Ser. No. 865,418, filed Oct. 10, 1969.

ZSM-8 can also be identified, in terms of mole ratios of oxides, asfollows:

and M is selected from the group consisting of a mixture of alkali metalcations, especially sodium, and tetraethylammonium cations.

ZSM-8 possesses a definite distinguishing crystalline structure havingthe following X-ray diffraction pattern:

TABLE 4 dA" l/l, l/l,, dA l 1.1 46 4 2.97 10.0 42 3 2.94 9.7 2 2.86 9.06 l 2.78 7.42 10 4 2.73 7.06 7 1 2.68 6.69 5 3 2.61 6.35 12 1 2.57 6.046 1 2.55 5.97 12 1 2.51 5.69 9 6 2.49 5.56 13 1 2.45 5.36 3 2 2.47 5.124 3 2.39 5.01 7 l 2.35 4.60 7 l 2.32 4.45 3 1 2.28 4.35 7 1 2.23 4.25 18l 2.20 4.07 20 l 2.17 4.00 10 1 2.12 3.85 100 1 2.11 3.82 57 1 2.08 3.751 2.06 3.71 6 2.01 3.64 26 6 1.99 3.59 2 2 1.95 3.47 6 2 1.91 3.43 9 31.87 3.39 5 1 1.84 3.34 18 2 1.82 3.31 8

Zeolite ZSM-8 can be suitably prepared by reacting a solution containingeither tetraethylammonium hydroxide or tetraethylammonium bromidetogether with sodium oxide, aluminum oxide, and an oxide of silica andwater.

The relative operable proportions of the various ingredients have notbeen fully determined and it is to be immediately understood that notany and all proportions of reactants will operate to produce the desiredzeolite. In fact, completely different zeolites can be preparedutilizing the same starting materials depending upon their relativeconcentration and reaction conditions as is set forth in U.S. Pat. No.3,308,069. In general, however, it has been found that whentetraethylammonium hydroxide is employed, ZSM-8 can be prepared fromsaid hydroxide, sodium oxide, aluminum oxide, silica and water byreacting said materials in such proportions that the forming solutionhas a composition in terms of mole ratios of oxides falling within thefollowing range SiO /Al O from about 10 to about 200Nap/tetraethylammonium hydroxide from about 0.05

Tetraethylammonium hydroxide/SiO from about 0.08 toIbo/tetraethylammonium hydroxide from about to about 200 Thereafter, thecrystals are separated from the liquid and recovered. Typical reactionconditions consist of heating the foregoing reaction mixture to atemperature of from about C to 175 C for a period of time of from about6 hours to 60 days. A more preferred temperature range is from about toC with the amount of time at a temperature in such range being fromabout 12 hours to 8 days.

The digestion of the gel particles is carried out until crystals form.The solid product is separated from the reaction medium, as by coolingthe whole to room temperature, filtering, and water washing.

The foregoing product is dried, e.g., at 230 F, for from about 8 to 24hours. Of course, milder conditions may be employed if desired, e.g.,room temperature under vacuum.

ZSM-8 is prepared utilizing materials which supply the appropriateoxide. Such compositions include sodium aluminate, alumina, sodiumsilicate, silica hydrosol, silica gel, silicic acid, sodium hydroxideand tetraethylammonium hydroxide. It will be understood that each oxidecomponent utilized in the reaction mixture can be supplied by one ormore initial reactants and they can be mixed together in any order. Forexample, sodium oxide can be supplied by an aqueous solution of sodiumhydroxide, or by an aqueous solution of sodium silicate,tetraethylammonium cation can be supplied by the bromide salt. Thereaction mixture can be prepared either batchwise or continuously.

The zeolites used in the instant invention can have the original cationsassociated therewith replaced by a wide variety of other cationsaccording to techniques well known in the art. Typical replacing cationswould include hydrogen, ammonium and metal cations including mixtures ofthe same.

Typical ion exchange techniques would be to contact the particularzeolite with a salt of the desired replacing cation or cations. Althougha wide variety of salts can be employed, particular preference is givento chlorides, nitrates and sulfates.

Representative ion exchange techniques are disclosed in a wide varietyof patents including U.S. Pat. No. 3,140,249; U.S. Pat. No. 3,140,251;and U.S. Pat. No. 3,140,253.

Following contact with the salt solution of the desired replacingcation, the zeolites are then preferably washed with water and dried ata temperature ranging from 150 F to about 600 F and thereafter calcinedin air or other inert gas at temperatures ranging from about 500 F to1500 F for periods of time ranging from 1 to 48 hours or more.

Prior to use, the zeolites should be dehydrated at least partially. Thiscan be done by heating to a temperature in the range of 200 to 600 C inan atmosphere, such as air, nitrogen,etc. and at atmospheric orsubatmospheric pressures for between 1 and 48 hours. Dehydration canalso be performed at lower temperatures merely by using a vacuum, but alonger time is required to obtain a sufficient amount of dehydration.

In a variation on the second column it may be desired to incorporate theZSM-S type zeolite with another material resistant to the temperaturesand other conditions employed in the separation processes. Such matrixmaterials include synthetic or naturally occurring substances as well asinorganic materials such as clays, silica and/or metal oxides. Thelatter may be either naturally occurring or in the form of gelatinousprecipitates or gels including mixtures of silica and metal oxides.

Naturally occurring clays which can be composited with the ZSM-S typezeolite include the montmorillonite and kaolin family, which familiesinclude the sub-bentonites, and the kaolins commonly known as DixieMcNamee-Georgia and Florida clays or others in which the main mineralconstituent is halloysite, kaolinite, dickite, nacrite, or anauxite.Such clays can be used in the raw state as originally mined or initiallysubjected to calcination, acid treatment or chemical modification.

In addition to the foregoing materials, the ZSM- type zeolite can becomposited with a porous matrix material such as silica-alumina,silica-magnesia, silica-zirconia, silica-thoria, silica-beryllia,silica-titania as well as ternary compositions such assilica-alumina-thoria, silica-alumina-zirconia, silicaalumina-magnesiaand silica-magnesia-zirconia. The matrix can be in the form of a cogel.The relative proportions of finely divided crystalline aluminosilicateZSM-S and inorganic oxide gel matrix vary widely with the crystallinealuminosilicate content ranging from about 1 to about 99 percent byweight and more usually, particularly when the composite is prepared inthe form of beads in therange of about 40 to about 90 percent by weightof the composite.

Another embodiment of this invention resides in subjecting the zeoliteZSM-S type to a mild steam treatment carried out at elevatedtemperatures of 800 F to 1,500 F and preferably at temperatures of aboutl,000 F to 1,400 F. The treatment may be accomplished in an atmosphereof 100 percent steam or in atmosphere consisting of steam and a gaswhich is substantially inert to the aluminosilicate. The steam treatmentapparently provides beneficial properties in the aluminosilicatecompositions and can be conducted before, after or in place of thecalcination treatment.

10 benzoate); and di-n-decylphthalate. Obviously, equivalent materialsmay also be used. In general, however, the second column may be said tocontain any stationary phase liquid partitioning agent as known in thechromatographic art.

The temperature at which the separations are carried out is important.it can be stated that the novel process of this invention can be carriedout out at temperatures ranging from about C. to about 250 C. It shouldbe noted that a wider temperature range can be employed but because ofthe possibility of catalytic conversion in the zeolite-containingcolumn, 250 C. appears to be a suitable upper limit. A more preferredtemperature range appears to be between about 100 to 200C. It is notedthat the above temperatures might vary slightly depending upon theparticular cationic form of the crystalline aluminosilicate zeoliteemployed but, in general, they represent operable parameters forcarrying out the novel process of this invention.

The carriers which may be employed are discussed hereinabove. Also, theprocess may be carried out in either a batch or continuous operation.The sorbed material can be subsequently recovered by conventionaldesorbing techniques such as thermal stripping, stripping with an inertgas, e.g., nitrogen, helium, etc. or evacuation or elutriation with asuitable polar or nonpolar stripping agent, e.g., water, n-hexane, etc.

The following examples will illustrate the best mode contemplated forcarrying out the present invention.

EXAMPLES 1-4 Typical preparations of ZSM-5 type zeolites are shown inthese examples. Examples l-3 show the preparation of the TABLE 6 30 g.NaAlO 281 g. sorbead fines 0.561b. NflAlOz- 13 g. NRAlOz.

Reaction composition 720 g. Ludox 3.311). TPABr solutl0n. 44.7 lb.Q-lbrand. 300 g. 40% 'IEAOH 1,025 g. of 2.2N TPAOH. 5.6 lb. TPABI 300 5.H2O.

16.71b. NaCL-.- 1,000 g. Ludox.

Reaction temperature C.) 100 100 193. Time (hr.) 168 168 327 144.

Washed dried at 230 F., calcined 16 hrs. at 1,000 F.

N H401 solution Base exchange:

Cone. (wt. percent) 25 5 25 25.

Temp. C.)

A similar treatment may be accomplished at lower temperatures andelevated pressures, e.g., 350-700 F. at 10 to about 200 atmospheres.

In the second column, there is maintained a gas-liquid chromatographicmedium, ordinarily employed for separation of 1 components as they passthrough a column with a carrier gas.

hydrogen form Z SM 5 and they involve the use of tetrapropylammoniumhydroxide (TPAOH) or bromide (T- PABr). Example 4 shows a typicalpreparation of the hydrogen form ZSM-8 using tetraethyl ammoniumhydroxide (TEAOl-l). Reaction conditions and results are shown in Table6.

EXAMPLE A first column eleven inches long and 0.5 inchesin diameter waspacked with 20 grams of ZSM-5 zeolite in the hydrogen form prepared inaccordance with the procedure of Example I and maintained at 180 C. Asecond column feet long and 0.50 inches in diameter was providedcontaining Tergitol NPX on Chromosorb P. The feed was 1.5 ml. of areformate of the following composition:

ethylbenzene 10 weight percent para-xylene 25 weight percent meta-xylene45 weight percent ortho-xylene weight percent This mixture was pumped tothe top of the first column (zeolite) at a pumping speed of 20 ml./hrs.and there admixed with steam, pumped at a rate of ml./hr. in avaporizer. The mixture was then passed through the zeolite-containingcolumn. Fractions were eluted from the column using a helium flow andwater as a stripping agent. After 2 minutes the first fraction wasrecovered which was 0.975 ml. of a mixture of 0.30 ml. ortho-xylene and0.675 ml. meta-xylene.

In the period of 3-5 minutes, there was eluted 0.375 ml. of para-xylenewhich analysis showed had a purity of 99%. Then, in the period of 5-8minutes, 0.15 ml. of ethylbenzene was eluted which analysis indicatedhad a purity of 99%.

The 0.975 ml. mixture of orthoand meta-xylenes was then.

passed to the top of the second column for contact with the TergitolNPX. Fractions were eluted from the bottom of this column in the samemanner. From this column, in the period of 9-12 minutes 0.675 ml. ofmeta-xylene was eluted which analyzed as 99% pure and in the period of13-14 minutes, 0.30 ml. of 99% pure ortho-xylene was eluted. Recovery ofeach component was essentially 100%.

The general description of the invention and the specific workingexamples illustrate the process as being carried out utilizing twoseparate columns, one containing the zeolite and the other containingthe partitioning agent. Quite obviously, however, the separationprocedure of the invention could also be effected in a single stagecolumn or chromatographic process which could contain combinations ofthe separation media. Thus in this embodiment, a single column would beutilized with the column containing the zeolite as the first separationmedium and the partitioning agent as the second separation medium.

The invention has been described herein with reference to certainpreferred embodiments. However, it is not to be considered as limitedthereto as obvious variations thereon will become apparent to thoseskilled in the art.

with a crystalline zeolite material having the X-ray diffraction patternset forth in Table l, separating in the column a mixture of meta-xyleneand ortho-xylene from the ethylbenzene and para-xylene which are sorbedat different respective rates by the zeolite, removing the mixture ofmeta-xylene and ortho-xylene, recovering the para-xylene followed by therecovery of the ethyl-benzene, passing the mixture of metaxylene andortho-xylene in contact with a partitioning liquid phase whereby saidmeta-xylene and ortho-xylene are sorbed at different rates, recoveringthe meta-xylene followed by recovery of the ortho-xylene.

2. A process according to claim 1 wherein the zeolite is ZSM-S.

3. A process according to claim 1 wherein the zeolite is ZSM-8.

4. A process according to claim 1 wherein said partitioning liquid phaseis selected from the group consisting of Tergitol NPX (nonyl phenolether of polyethylene glycol), m-bis (mphenoxy-phenoxy) benzene and 2percent squalane, UCON 1840, UCON LB-SSOX, di-n-propyltetrachlorophthalate, squalane, 40 percent 1,2,3 tris(2-cyanoethyoxy)propane and 60 percent oxybis (2-ethylbenzoate) and di-n-decylphthalate.

5. A process according to claim 4 wherein the zeolite and partitioningliquid are maintained in columns through which the mixture is passed.

6. A process according to claim 5 wherein the column containing theliquid has a diameter about twenty times greater than the zeolitecolumn.

7. A process according to claim 6 wherein a carrier is admixed with themixture prior to passage through the columns.

8. A process according to claim 7 wherein the carrier is selected fromthe group consisting of steam, water, nitrogen, air, helium, hydrogen,hydrocarbons, alcohols, ketones and mixtures thereof.

9. A process according to claim 8 wherein the temperature UNITED STATESPATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 656 ,278 DatedApril 18 1972 Inventor(s) B. M. 'Drinkard It is certified that errorappears in the above-identified patent and that said Letters Patent arehereby corrected as shown below:

Column 2, line 14 "by" should be be Columh 5, line 49, the columnheadedJAgNO "4.46" should be 7.46

Signed and sealed this 26th day of December 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR.

ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents '"ORMPO-105O (10-69) USCOMM-UC GDBIG-PBQ r HTS GOVERNMENT Pmm'mc, orrscr 1999'1366-334

2. A process according to claim 1 wherein the zeolite is ZSM-5.
 3. Aprocess according to claim 1 wherein the zeolite is ZSM-8.
 4. A processaccording to claim 1 wherein said partitioning liquid phase is selectedfrom the group consisting of Tergitol NPX (nonyl phenol ether ofpolyethylene glycol), m-bis (m-phenoxy-phenoxy) benzene and 2 percentsqualane, UCON 1840, UCON LB-550X, di-n-propyl tetrachlorophthalate,squalane, 40 percent 1,2,3 tris(2-cyanoethyoxy) propane and 60 percentoxybis (2-ethylbenzoate) and di-n-decylphthalate.
 5. A process accordingto claim 4 wherein the zeolite and partitioning liquid are maintained incolumns through which the mixture is passed.
 6. A process according toclaim 5 wherein the column containing the liquid has a diameter abouttwenty times greater than the zeolite column.
 7. A process according toclaim 6 wherein a carrier is admixed with the mixture prior to passagethrough the columns.
 8. A process according to claim 7 wherein thecarrier is selected from the group consisting of steam, water, nitrogen,air, helium, hydrogen, hydrocarbons, alcohols, ketones and mixturesthereof.
 9. A process according to claim 8 wherein the temperaturemaintained in the column is about 25*-300* C.
 10. A process according toclaim 9 wherein the sorbed materials are recovered by desorbing.
 11. Aprocess according to claim 10 wherein the mixture contains about 5-15weight percent ethylbenzene, 20-30 weight percent para-xylene, 40-50weight percent meta-xylene and 15-25 weight percent ortho-xylene.
 12. Aprocess according to claim 11 wherein the zeolite is selected from thegroup consisting of ZSM-5 and ZSM-8 and the partitioning liquid isTergitol NPX.